All electronic line finder and selector system



Dec. 13, 1949 D. H. RANSOM 2,490,833

ALL ELECTRONIC LINE FINDER AND SELECTOR SYSTEM Filed April 26, 1947 6 Sheets-Sheet 1 DIVWER 500 CYCLES DNlDER DNNBER IO KC ww-ll- N 5 N 3, H 1mg 9 g M? UM 4 J F a V 3 g u 9 M k a E N 9 INVENTOR.

N 1 an /0 0411/50/ 1 A TTOENEY Dec. 13, 1949 RANSOM 2,490,833

ALL ELECTRONIC LINE FINDER AND SELECTOR SYSTEM A TTOPNEY' 1949 D. H. RANSOM ALL ELECTRONIC LINE FINDER AND SELECTOR SYSTEM 6 Sheets-Sheet 3 Filed April 26, 1947 INVENTOR. DAV/0 fl. lPflA/SOM ATTORNEY Dec. 13, 1949 D. H. RANSOM ALL ELECTRONIC LINE FINDER AND SELECTOR SYSTEM Filed April 26, 1947 6 Sheets-Sheet 4 LOCK-\N 0SC\LLATOR 200mm soxc I N CUPPER It D\FFERENT\A- TING cmcun 'PH ASE CORECYOR 29 l 7 SYNCH D.

MUL'H' V\BRATOR gfgz AMPUHER I70 7 A w .L

INVENTOR.

ATTORNEY Dec. 13, 1949 D. H. RANSOM $490,833

ALL ELECTRONIC LINE FINI DER AND SELECTOR SYSTEM Filed April 26, 1947 6 Sheets-Sheet 5 LOCK-IN OSCILLATOR RlNG\NG OSClLLATOR INVENTOR. DAV/D ll. Rfl/VSOM ATTORNEY -Dec. 13, 1949 D. H. RANSOM 2,490,833

ALL ELECTRONIC LINE FINDER AND SELECTOR SYSTEM Filed April 26, 1947 6 Sheets-Sheet 6 90 PHASER w KC DlAL UNK IN V EN TOR. DAV/0 h. RIM/50M Patented 1 949 i ALL ELECTRONIC LINE FINDER AND I SELEGTOR'SYSTEM I David Hiram Ransom, London, England, assignor to Federal'Telecommunicatlon Labs., Inc., New York, N. Y., acorpora'tlon of Delaware Ap ueauon -u 2c, 1947. Serial No. 744,111

acclai rive-4s) This invention relates'to new and useful improvements in telecommunicationswitching sysequipment of a dial link;

tems and, more particularly, to systems in which all or most of the switching operations are per 1 formed by electronic as distinguished from electromechanical switchingdevices.

The present is an improvement of. the

Patent No. 2,462,896, Marchl, 1949; 628,611, filed November 14, 1945; 643,285., filedJanuary 25, 1946; 646,169, filed February 7, 1946; 648,758, filed Febsystem. disclosed in my copendlng applications, Serial and Nos. 628,610, filed November 14, 1945,.issued U. S. v

ruary 19, 1946; 654,271, filed March 14, 1946, and

the applications referred to therein.

The objects of the present invention are to increase the flexibility 0f the system,xthus making possible its expansion into or connection with large switching systems, and to reduce theequipment which is held busy duringconversation to a minimum.

With these objects'in view, when-an electronic line finder seizes a calling line or, as stated in my prior applications, locks into a calling line, then one of a plurality of links becomes appropriated for the connection with which a register becomes associated only during the building up of the connection and is released once the called line is seized.

According to one feature of the present invention, each link has a line finder for locking into the calling line and also a selector for locking into the called line, theselector being controlled in accordance with the designation of the called line by means associated with the link only during the building up of the connection.

A constantly operating cathode ray distributor is provided for associating the lines with a selected link for rapidly recurring brief periods of time, and another cathode ray tube distributor is'employed for identifying the selected link.

According to another feature of the invention,

the means for signaling, e. g. ringing, the called line is associated with the selector.

This and other features of the invention will Fig. 1 shows one subscriber's line and the equipment common to a group of twenty lines;

Fig. 2 illustrates a link finder of the-dial link equipment;

,Fig. 7 is a block diagram indicating the-relationship between the various circuits. The subscriber's line equipment comprises a substation set I, a hybrid coil 2 with a suitable low pass filter, a dial 3 which is arranged to send'dialing pulses by cutting a resistance 4 in series with the line, and a balancing network 5. The subscribers set comprises a gas tube relay. adjusted to operate at voice frequency.

The central exchange equipmentcomprises two continuously operating distributors; a sending tube 6 and a receiving tube 1. These are cathode ray tubes of the kind whose beams are arranged to rotate at 10 kc. per second successively to engage twenty dynode electrodes in which the twenty subscribers line circuits terminate. A thirdsuch distributor type of cathode ray tube which is common' to the group of twenty lines is indicated at 8 and is provided with dynodes in which the'links or trunks accessible to the various subscribers terminate. Busy test circuits complete the common equipment.

In Fig. '7, the common equipment for twenty lines (Fig. 1), is indicated in rectangle 9. The I subscribers link circuit (Figs. 4 and 5) is shown at Ill and dial link (Figs. 2, 3 and ,6) at II. This general set up will help in following the complete circuit diagram. 1 I

A plurality of links is provided at the central exchange. Upon the initiation of a call the line finder of Fig. 4 locks into, i. e. becomes connected with, the calling line, and thus selects a link for the connection. The pulse generator S'identifies the selected link and the line finder which was taken into use. Each line finder has means associated with it for establishing the talking connection. The line finder and the talking equipment are shown, respectively, above and below the dottedline in Fig. 4. z Link finder equipment shownin Fig. 2 connects with the selected link the dial link or register equipment H (Fig. 7 and Figs. 2, 3 and 6) for receiving and registering the digits of the called number.

In addition to the talking equipment, each line finderlFig. 4) and link has associated with it also selector equipment (Fig. 5) which receives the in- T v, orr c z pulse and sequence by which the y formation as to the identity of the galled line from the dial link and locks the calledline to the selected link.

The ringing of the called line is controlled from the selector circuit (Fig. as is the opening of the talking gate (Fig. 4).

The dial link comprises dial pulse forming and timing circuits, shown in Fig. 3, which form the pulses from the breaks in the pulse trains sent group and units digit registers consisting of paired cathode ray tubes I3, I 3' and l5, l5.

The dial link (Figs. 2, 3 and 6) is used only during the establishment of the connection and is released when the called subscriber answers. Only equipment shown in Figs. 1, 4 and 5 is employed during conversation between the calling and called parties. 7

We shall now trace the establishment of a connection.

when a subscriber at a station like i initiates a call, a negative potential is applied to the dynodes in tubes 6 and i in which the line terminates. This negative potential will be conveyed via the anode ll of tube 1 to the grid of a cathode follower and inverter tube IB. From the cathode of tube 1 8 the negative pulse will be applied to the grid of a clipper tube l9, and the positive pulse appearing in the anode circuit of tube l3. to the grid of clipper 20. Clipper tube 2U will apply a negative pulse to the grid of a cathode follower 2|. From the cathode circuit of tube 2| the amplified negative pulse will be applied over conductor 22 to all the subscribers link circuits which, as indicated in Fig. l, are all multipled together.

The clipper amplifier i9 is normally biased to draw current and the signal amplitude is so ad- Justed that each negative impulse applied to its 811d will drive it beyond cut-off, clipping the variation produced by transmitter modulation or dial pulse. The positive plate output of i9 is fed also to the grid of cathode follower 25, and the positive pulses appearing in the cathode circuit thereof are fed over conducter 24 to the grids of all the line finder gate tubes 23 which are connected in multiple.

The tubes 23 are normally biased far enough beyond cut-oil so that the signal applied to their grids will not affect their plate output. A lock-in oscillator 26 in each line finder operates atafrequency slightly less than the scanning frequency of master oscillator 21 (200 kc.) contion. The trailing edge of the diflerentiated pulse obtained from the differentiating network 3! is suppressed.

The negative pulse is passed through a cathode follower 32 to the cathode of the line finder gate tube 23, but the amplitude of the pulse is adjusted by the delayed gain tube 33 so that normally the 1 line finder gate tube 23 will remain cut off. This tube thus has a negative pulse applied to its cathode and a positive pulse to its grid, neither of which "is strong enough to drive it beyond cut-ofl. Since, however, the frequency of the line finder lock-in oscillator 26 is slightly less than that of 'the master oscillator 21, the negative and positive pulses applied to line finder gate 23 will drift until they occur simultaneously. When this happens, gate 23 will be opened to pass a negative pulse through its plate circuitto a rectified tube called line selector circuit (Fig. 6), including a ductor 38.

34 and an integrating network 35 to drive a gate control tube 38 beyond cut-on, permitting a lockin gate 31 to open and pass a signal applied to its grid from the master oscillator 21 over a con- From the plate of the lock-in gate 31 the pulse is applied over a phase corrector 33 to the oscillator 26, synchronizing the latter with the master oscillator 21.

A portion of the rectified output of diode. is fed to the grid of delayed gain tube 33 which is driven beyond cut-ofl after a fewimpulses, causing release tube to become conductive. Since the plate resistor 4| of this tube is common with the screen of clipper gate 30, the screen will cause the grid of the line finder gate to be line.

driven positive by the pulse applied thereto over conductor 24, and clipping by grid current will occur, reducing the signal amplitude of the incoming pulse to a value insufilcient to affect any other link. 1

The negative plate output of the line finder gate 23 is applied also over conductor 42 to the grid of a gain control tube 43 controlling the effective connection of the calling line with the talking circuit. The positive pulses thusproduced in the plate circuit of 43 are applied in parallel to the suppressor grids of an input gate tube 44 and output gate tube 45 which are normally biased to cut-off by the plate resistor 46 of tube 43. The negative pulse applied over conductor 42 will drive the grid of 43 beyond cut-off reducing the voltage drop across its plate resistor 46 to zero. This raises the Mason the suppressor grids of 44 and 45 and permits signals applied to their control grids to pass, and thus afiords a channel for signaling from the calling clipping action of tube is will cut ofl the modutrolling the rotation of the beams in 6 and I.

The output of 26 is divided to a frequency of approximately 50' kc. and the resulting sine wave is passed through a clipper amplifier and differentiating circuit 28 to a multi-vibrator 29 arranged to synchronize at approximately 10 kc The output of the multi-vibrator 29 is differentiated in a circuit 3! and applied to the grid circuit oi a-clipper tube 30. The constants and the bias oi this'tube'are adjusted to cause the leading edge'of the difierentiated pulse to produce in the plate circuit of tube 3G a short, square negative pulse of approximately 5 micro-seconds duralated portion of the signal so that the positive pulses applied to the grid of the line finder gate 23 will be uniform, irrespective of dial or microphone modulation. However, the clipper tube 23 is biased so that only the modulated portion of the positive pulses applied to its grid from the plate of the inverter it will produce negative pulses in the plate circuit of 20 and the grid of cathode follower 2i. The output of 21 will represent, therefore, the modulated pulses which are applied over conductors 22, 41 to the control grid of the input gate tube 44 (Fig. 4) in parallel to the control grid-of dial pulseg'ate tube 43 (Fig. '2 H As soon as the line finder lock-in oscillator 28 has been synchronized by the calling signal, a negative pulse is transmitted from the plate of the line finder gate tube 23 over conductor 49 to the control grid of a dial link selector gate 58 (Fig. This tube is biased to pass a signal until the called line selection equipment of Fig. 5 is locked to the subscriber's link and thus to the called line. The positive pulses appearing in the plate circuit of gate 50 are fed over a conductor 5| to the control grids of the make-busy tubes 52 (Fig. 1) of all the dial links which are multipled to conductor 5|. This is an indication to all the dial links that a particular subscriber's link has become associated with a calling line and that, therefore. the register circuits must be prepared to take and store pulses sent from the calling line via said particular link and representing the number of the called subscriber.

The dial link (Fig. 2) comprises a finder circuit similar to the subscribers line finder circuit of Fig. 4. A lock-in oscillator 53 operating at a frequency slightly less than the master oscillator 21 (200 kc.) supplies its output to a clipper and differentiating network 54 and thence to a multivibrator 55 arranged to synchronize at kc. The output of 55 is difierentiated in network 56 and applied to the control grid of a clipper gate tube 51. The constants and bias of this tube are adjusted to produce from the leading edge of the difierentiated output of multi-vibrator 55 a short, square negative pulse of approximately 5 micro-seconds duration. The trailing edge is suppressed. This negative pulse is passed through a cathode follower 58 to the cathode of dial link finder 59. As in the case of the line finder, the amplitude of the pulse passing through gate 51 is adjusted by delay gain tube 60 so that normally the link finder gate 59 remains cut off.

It will be seen, therefore, that the dial link finder gate 59, just as the line finder gate tube 23, receives two signals; a positive pulse on its grid applied under the control of the master oscillator 21, via 23, 50 and the dial link make-busy tube 52, and a negative pulse on its cathode from the lock-in oscillator 53, via 51, 58. Neither pulse alone will drive gate 59 beyond cut-off to conduction, and only that particular gate 59 can be operated whose dial link is connected with the calling subscribers link.

The frequency of the oscillator 53 being slightly less than that of oscillator 21, the two will drift until a coincidence occurs which will cause the gate tube 59 to pass a negative signal on its plate over a rectifier 6| and an integrating network 62. A gate control tube 63 will be driven to cut-oil after a few pulses, permitting a lock-in gate 64 to pass a signal from master oscillator 21 over conductor 65, the plate of 64, and a phase corrector network 66 to the oscillator 53 and synchronize the two oscillators.

A portion of the output of network 52 is applied to the grid of the delayed gain tube 60 which is driven to cut-oil? after a few pulses, causing a tube 61 to become conductive. The plate resistor of the delayed gain tube 60 is common with the screen grid of the clipper gate tube 51 whose screen voltage will, therefore, rise and increase the amplitude of the negative pulse which is applied as a pedestal pulse to the cathode of the finder gate 59. This will cause the grid of tube 59 to be driven positive by the positive pulse applied thereto over conductor 68 from the cathode of the make-busy tube 52 and clipping by grid current 6 will occur. The signal amplitude of the pulse over conductor 68 will be reduced to a value which is insufilcient to aflect the dial link finder tube 59 of another dial link finder connected in multiple, since their cathodes do not receive properly timed pedestal pulses. The plate output of the gate tube 59 controls a tube 69 which, in turn, controls the dial pulse gate tube 48 through which the dial pulses are sent from the calling line to the register.

Normally a series of pulses will be passed from the pulse separating circuits (Fig. 1) comprising clipper tube 20 and cathode follower 2| over conductor 22 to the dial pulse gate tube 48 to control the forming and relaying of the dial pulses. The selective action of the input clipper tube 20 interrupts the pulses with each pulse from the subscriber's dial 3. The positive pulses appearing in the output circuit of the gate tube 48 are applied over a conductor 10 to the grid of an amplifier tube ll after the associated network has shaped them to form square waves. The amplified negative pulses are again shaped in a network 12 before they are applied to the grid of a second amplifier tube 13, are then differentiated in a network 14 and applied to the grid of a triode 15 which, with a second triode I6,

forms the dial pulse generator fiip-fiop circuit in which tube 18 is normally conducting. The leading edge of each of the differentiated dial pulses in the output of circuit I4 flips conduction from tube 15 to tube 16 for a period determined by the circuit constants, whereby a timed positive pulse will be produced by the pulse generator and applied to conductor 11 and therethrough to the control grid of a gate tube 18 controlling the registering of the first or group digit.

The switching tube I2 is so adjusted that its beam is normally centered on the No. 1 dynode causing a positive potential to be applied over conductor 19 to the suppressor grid of the group digit gate 18. The first series of dial pulses produced at the calling station, as reproduced in the dial pulse generator (Fig. 3), will, therefore, be sent over conductor H to the control grid of 18 and appear as negative pulses in the plate circuit of 18. These are applied over a network 86 to a rectifier and limiter 8|, whose output will charge deflecting plates 84 and a condenser 82 which is connected with anode 83 of the group digit register tube I3. This will cause the stepby-step advance of the beam of tube l3. Normally this beam is centered, as shown in Fig. 6, in the first dynode opening. As the charge leaks oil the condenser the beam will fall on the edge of the opening where equilibrium is established between the beam and the leakage currents.

Upon the completion of the first or group digit pulses, the beam of the switching tube 12 is moved to its second dynode in the following manner:

The dial pulses formed in the integrating circuit and amplifiers 'Hl3 (Fig. 3) are passed over a conductor 85 to a second integrating network 86 connected with the grid of triode 81 which, together with a second triode 88, forms a fiip-fiop circuit, with 88 normally conducting. This circuit constitutes the digit pulse generator. The integrated dial pulses will cause 81 to become conductin for the portion of the series of pulses representing one digit. An ineffective negative pulse is generated at the beginning of a series of pulses in a difierentiating network 89 and thence to a transfer pulse generator com- I ister sweeps over a single dynode.

7 prising triodes 90. and 92, forming a flip-flop circuit in which 92 is normally conducting.

In the transfer pulse generator the tube 90 is made conducting for a period of time determined by the circuit constantsand generates a timed negative pulse which indicates the termination of the dialing of the first digit. This pulse is fed over conductor 93 to a rectifier and limiter 94 which will charge a condenser 95 and thus affect the deflecting plates 96 of the beam tube I2 to move its beam from dynode I to dynode No. 2.

When the beam is centered on dynode 2 positive potential will be applied over conductor 91 to the suppressor grid of units digit gate 98. This gate will, therefore, pass the dial pulses which are applied to its control grid over conductor 11 from the dial pulse enerator I5, I6. The units digit pulses appearing in the plate circuit of gate 98 are then applied through an integrating network 99 to limiters I to step the beam of units digit tube I by a number of steps c. rresponding to the units pulses.

Once again the digit pulse generator 81, 80 operates at the end of the units digit and causes the operation of the transfer pulse generator 90, 92 which, over conductor 93, will apply a timed negative pulse to the limiters 94 and operate the control circuit switching tube I2 to center its beam on dynode No. 3.

The dialing operation is now completed and pulses will be generated in the register digit tubes I3, I3 and I5, I5 in accordance with their setting by the pulses which were dialed.

The beam of tube I3 is rotated at kc. under the control of a 90 phaser IOI which is controlled over conductor I02 from the lD-kc. frequency divider (Fig. 1) in the control equipment of the distributors 6 and I, insuring thus the rotation of the beams of all these tubes at the same rate. The beam of tube I3 contacts each of the four dynodes I03 for a period corresponding to the period required by the beams of distributor tubes 6 and I to sweep over five of their dynodes, the assumption being that twenty lines are divided into four groups of five. Thus, a pulse will be generated to designate a particular one of the four groups of five lines and will be applied to the dynodes of all the tubes I3.

The beam tube I5 in the units digit register is rotated at 50 kc. per second under the control of a 90 phase changer I04 which is controlled over conductor I05 from the 50-kc. frequency divider in the control equipment (Fig. l) of the distributors 6 and I. The beam of tube I5 will. therefore, sweep over five of its dynodes, such as I06, while the beam of tube I3 in the group reg- Units pulses will be generated of the proper time duration and will be applied to the dynodes if all the units digit beam tubes I5 provided for the various links.

Negative pulses produced by the beams of tubes I3 and I5' will be transferred to the common anodes I01 and I08, respectively, of the tubes I3 and I5 whose beams are centered on the proper dynodes. The negative pulse on anode I01 will, through an inverter I09, be applied as a positive pulse to the control grid of a pulse gate I I0. The suppressor grid of this gat tube will be similarly pulsed over a differentiating network III in the output circuit of an inverter I I2 whose 'control grid receives negative pulses from the common anode I08 of units digit tube IS. The negative pulses appearing in the output circuit of pulse gate IIO identify, therefore, the time position of the called line.

. 8 When, upon the completion of the dialing, the beam of the control circuit switching tube I2 was advanced onto dynode 3, it applied over conductor I I3 a pulse to the suppressor grid of busy test gate H4. If the called line is idle, then the control grid of gate 4 is positively biased, whereby a single negative pulse will be transmitted to the control grid of an inverter H5 which, in turn, will transmit a positive pulse to the transfer pulse generator 90, 92. When this functions, it will transmit a negative pulse over conductor 93 to advance the beam of the switching tube I2 onto dynode 4. i

If, however, the called line is busy, then the control grid of busy test gate I I4 is biased to cutoff to block the call by preventing the moving of the beam of tube I2 into position 4. This is accomplished under the control of a busy test tube H5 in the subscribers common circuit (Fig. 1). In a manner to be described below, positive pulses will be generated on the cathode of tube H6 if the called line is busy, and will be transmitted over conductor III to th control grid of a busy test tube II8 (Fig, 3) which is biased to cut-off. The negative pulse identifying the called line is fed from the plate of pulse gate III) (Fig. 6) over conductor H9 and then through an inverter I20 to the suppressor grid of busy test tube H8. When these two positive pulses are simultaneously applied to the control and suppressor grids of H6, this tube will generat a negative pulse in its plate circuit which, after integration, will actuate a stop pulse generator comprising tubes I2I and I22. The pulse generator is a flip-flop circuit, with I2I normally conducting. The integrated pulses will flip conduction to tube I22 which, in turn, will apply a negative pulse to the control grid of busy test gate I I4 to block the call as above described.

Assuming, however, that the called line is idle and that, therefore, the beam of the switching tube I2 has been moved into position 4, it will apply over conductor I23 a positive pulse to the suppressor grid of selection pulse gate I24 (Fig. 2) to bias it to conduction whenever a negative pulse is applied to its control grid over conductor II9 from pulse gate H0 which. as above stated, identifies and now permits the locking-in of the called line in the following manner:

Whenever tube I24 is conducting called line selecting bursts of positive pulses are passed over conductor I25 to the control grid of selection pulse test tube I26 (Fig. l) in every link. The cathode output of I26 is fed over conductor I2I to the control grid of the selection synchronizing gate tube I28 (Fig. 5). If the positive pulses are received on the control grid of tube I28 at the same time as those sent over conductor I29 to the screen grid of I28 by generator 8 and which identify the subscribers link, and if these two pulses coincide with the negative signal appearing on the cathode of the selection synchronizing tube I28, then a negative pulse will be passed from the plate of I 28 to a rectifier I30 and an integrating network in the grid circuit of the selection synchronizing control flip-flop circuit.

The link identification pulse generator 8 has its beam rotated at 500 cycles per second under the control of a phaser I3I and a frequency divider I32 which is fed from the frequency divider oi the common equipment of tubes 6 and I. Whenever the beam of tube 8 sweeps over the dynode appertaining to the link to which the calling line has been locked, the positive pulse applied to conductor I33 will reach the control grid .the dial link selector gate 58 which identifies the link with which the calling line is associated because the line finder 23 is locked thereto. The gate I34 is thus biased to conduction and amplifled negative pulses appearing in its plate circuit are applied over conductor I35 to the control grid of an identification pulse tube I36 in the link circuit (Fig. 1). g

. Each subscribers link is represented by an identification pulse which is long as compared with the repetition rate of the signal pulses. In the present case, it is assumed that the identification pulse is twenty times as long as the signal pulse. Therefore, twenty signal pulses will be fed over conductor I35 to the control grid of the identification pulsetube I36 (Fig. 1) while the beam of link identification pulse generator 8 is passing over the dynode representing the link with which this particular tube I36 is associated.

tube I36, and of each such identification pulse tube associated with the other links, is fed over The cathode output of the identification pulse engages the dynode of the selected link, the positive pulses will appear at the same time in the pulsed over conductors 22 and 68. While the link identification pulse persists, gate I39 will pass a signal over an integrating network to the control grid of identification control tube I48 which is normally conducting. The integrated signal will flip conduction to tube MI and, when the signal ceases, the action will be reversed. The resultant output of the identification control circuit I48, I willbe applied to the control grid of the selection pulse gate I24 which, as above stated, will compare it with the signal received in position 4 of the switching tube I2 (Fig. 3).

We have seen that the selection synchronizing control circuit (Fig. 5) receives the output of the pentode I28 which compares the pulses produced by the selection pulse gate I24 (Fig. 2), received via I28, with the pulses produced by the generator 8 (Fig. 1). The two triodes I42 and I43 (Fig. 5) of the selection synchronizing control are connected in a flip-flop circuit;

The cathode of the selection synchronizing gate I28 is fed with pulses generated in a. ZOO-kc. lockin oscillator I44 (Fig. 5). The lock-in oscillator I 44 operates in a manner similar to the lock-in oscillators 28 and 53 of the line and link finder circuits. Its frequency is slightly less than that of the master oscillator 21 so that there is a drift between the two. The output is divided to 50 kc. and is fed through a clipper and differentiating circuit I45, a 10-kc. synchronizing multi-vibrator I46, and a differentiating network I4I to the control grid of a clipper gate tube I48. The leading edge of the differentiated 10-kc. pulses are clipped and amplified in this tube, and the trailing edge is suppressed, generating in the plate output of I48 a negative selection pulse of approximately five microseconds duration. These pulses are passed by a cathode follower I49 to the cathode of the selection synchronizin tube I28.

' 10 Three signals will, therefore, be applied to the selectlonsynchronizing gate I28, i. e. (1) negative pulses applied from the lock-in oscillator I 44 to the cathode, (2) positive pulses applied to the control grid in position 4 of theswitching tube I2 via I24, I28 and conductor I21, and (3) positive pulses applied to the suppressor grid from the dynode of the pulse generator 8 via conductor I29. When these three signals occur simultaneously, then a negative plate signal is'passed to the rectifier I38 which builds up a potential on the control grid of I42 to flip the conduction to the normally non-conducting tube I48. This, in turn, puts out a negative pulse which flips conduction from a tube I58 to tube I5I in a selection gate control flip-flop circuit. The latter biases the control grid of a lock-in gate tube I52 which, through a phase correcting network I58, synchronizes the lock-in oscillator I 44 with the master oscillator 21 which is connected with the suppressor grid of the lock-in gate I52 over a conductor I54 which is multipled to the conductors 38 (Fig. 1) of all the links.

Thus, the negative called line gate pulses are produced in the output of the clipper gate I48 in the same manner as was described in connection with the clipper gates 51 and 38 of the line and link finder circuits. Thesenegative pulses are not only passed through the cathode follower circuit of I49 but are also inverted by this tube and applied to the control grid-of 8. called line control tube I55 whose suppressor grid is biased to conduction by the selection gate control circuit I58, I5I. Whenever I55 passes a negative pulse over its plate circuit and a conductor I58 to the control grid of a called gate control tube I51 (Fig. 4) then this tube will open the input gate I58 and the output gate I59 in the talking equipment as will be explained below.

The selection gate control circuit I 58, I5I (Fig. I

5) also applies a bias potential to the suppressor grid of the dial link selector gate 58 to cut oil the selecting signals which this gate applied over conductor 5I to the dial link make-busy tube 52. Therefore, the application of positive pulses again become conducting. 63 will first cut ofl the lock-in gate 84 so that the associated. oscillator 53 may again drift in time. The release control tube 88- causes the sending of a pulse from the plate of the associated tube 61 which is applied over conductor I68 to the control grid of a triode I8I (Fig. 3) for restoring to normal the beam switching tube I 2. The pulse is applied also over conductor I 62 to the control grids of the release tubes. I63 and I84 (Fig. 8) to control the restoration to normal of the beams of the group and unit digit registers, respectiveLv.

The dial link and associated register may now be used for the building of another connection.

When the lock-in gate I52 (Fig. 5) functions. the pulses from the selection synchronizing control I42, I 43, which flips the selection gate control I58, I5I, flips also the ringing gate control circuit comprising triodes I65, I66. Normally I66 is triggered so that I conducts and biases ringing gate control tube I6I which permits ringing signals to pass from ringing oscillator. I68 over conductor I69 to the control grid of output gate IE9. 'T'hr'n'lin'h IBQ thn si nal nnscn via. can run.

plifierl'lll, conductor the-sendin distributor 8. The distributor is normally cut oil! by the bias on its grid so "the called line will then stop. r Conversation may now take place between the calling and called lines. The talking channel may 11 III, to'the controlgrid or that a signal applied thereto over. conductor;

1 I'll drives it'to conductiononly when its beam passes the dynodein which the called line ter- ;minates. The modulation applied by the ringing oscillator I88 to the signal pulses actuates.

a a gas relay in the, subsetot vthe'called subscriber which, in turn, operates a visualor audible signal;

when the called subscriber answers, the reconnection with the initiation of-a call, from the calling line.

control grid 01' the input gate Ill.-. The input gate will,'thereIorebe-opened only during the called lineperiod by the pulses applied to its suppressor gridirom the fcalled gatecontrol tube I51. The application of the signals'will continue until the ringing gate controlcircuit is flipped from It! back to I66 and cuts of! the ringing gate tube I 81. The application of the ringing current to be traced-from the calling line dynode. in the receiving distributor the *anode' I1 of this distributor, the cathode follower and inverter it, the clipper amplifier 20,, the cathode follower I 2!, conductor 41, the input gate 44 in the asso- I elated line finder link, and thence through, a low pass filter 112, the output gate I59,'amplifier no, conductor "I, to the gridot the sending distributor 6 and the dynode in which the called .ceiving distributor will,when passing the dynode' in which the called line terminates, generate. pulses in the same manner as was described in 1 I These pulses will be passed through- -the-cathode follower ii and conductor 41 to the for each line operable in accordance with the number 01' the called lines, a cathode ray tube having electrodes in which said lines terminate,

means tor-causing the beam of said tube to sweep over said electrodes; 'a plurality of normally inactive electronic line'finders, alink associated with "each linefinder. means responsive to the initiation of a calltor actuating a line finder to connect the calling line with the associated link when- 10 ever the beam of the tube engages the terminals oi' the line, a normally inactive-electronic selector for each link, impulse responsive means variably operated under the control of the calling device for controlling said selectorsand means for actuating the selector of the selected link whenever the beam or the tube called line.

2. The system according to claim 1, and means engages the terminals or the I operable when the called line answers for releasing the impulse responsive means. j

3. The system according to claim '1, means associated with each selector for signaling the called line, and means jointly controlled by the impulse responsivemeans and the called line for operating the last-mentioned means.

4.The system according to-claim 1, and electronic means for associating the impulse responsive means with the link of the actuated line finder. I

5. The system according to claim 1, electronic switching-means for each line finder to establish two-way talking connection'over the associated link, and means jointly controlled by the actuated line terminates, and thence through the hybrid coil 2 in the called line to thecalled subset. The channel in the opposite direction is the. same, except that it is efiective when the beam of line finder and selector for actuating the-switching means whenever the beam of the tube sweeps over the terminals ot'the calling and called lines.

6. In a telephone exchange system, a plurality of numerically designated lines, a calling device for each line operable in accordance with thenumber of the called line, a cathode ray tube having electrodes in which said lines terminate,

the distributor 1 passes over the dynode oi the called line, and the beam of the distributor 6 passes over the dynode of the calling line, and

the gate timing is controlled by I58 and overs.

low pass filter I13.

when the called subscriber answers, no new I call be initiated because a busy pulse shaper j i'liiliig. 1) will apply positive pulses to thegrid of busy 'gate I16 when it receives negative pulses over conductors Ill and I55 from the called line control gate I55 (Fig. 5); Busy gate I16 will,

means for causing the'beam or said tube to sweep over said electrodes, a plurality of normally inac-.

. tive electronic line finders, a link associated with each line finder, means responsive to the initiation of a call for actuating a line finder whenever the beam of the tube engages the terminals of the calling line, a normally inactive electronic selector foreach link, normally inactive means variably operated under the control of the calling device 7 and controlling said selectors, means for associating the last-mentioned means with the sethereiore, apply negative pulses to conductor 24 tube36 (Fig. 4) will again become conductive and render conductive the delayed gain tube 33 which will cut ofithe release tube 40 and cause the sendingoi anegative pulse over conductor I'M to [the selection gate control circuit I50, ISI- (Fig. 5)

- f restoring it tonormal with ISI conducting.

" .-The.lock-in gate I52 and the dial link selector I gate are then restored to normal and the subscribers link'is prepared to receive the next call. a

-What I claim is:

t 1. In a telephone exchange system, a plurality of numerically designated lines, a calling device which prevent theloperation of any linefinder gate 23. The positive pulses from the shaper I'Iiareapplied'also to the suppressor grid'oi busy test tube IIS with consequences already lected link, and means for actuating the selector oi the last-mentioned link whenever the beam of the tube engages the terminals of the called line.

In a telephone exchangesystem, aplurality I of numerically designated lines, a calling device (or each line operable in accordance with the number of the called line, a cathode ray tube havingjelectrodes in which said lines terminate; means for causing the beam of said. tube to sweep over said electrodes, a plurality or normally inactive electronic line finders, alink associated with each.

line finder, means responsive to the initiation of a call for actuating a line finder to connect the calling line with the associated link whenever the beam of the tube engages the terminals of the line, a normally inactive electronic selector for each link, a plurality of registers variably operable under the control of a calling device and controlling said selectors, an electronic link finder associated with each register means for actuating a 7 link finder forconnecting the associated register with the link of the actuated line finder, and

means controlled by the actuated register for ac- 13 tuating the selector of the link of the actuated line finder whenever the beam of the tube errgages the terminals of the called line.

8. The system according to claim 7, and in which the link finder comprises a normally blocked electric discharge device having anode, cathode and grid electrodes, a grid circuit for said device controlled by the actuated line finder, an oscillator associated with the link finder, means for synchronizing said oscillator with the sweep of the cathode ray tube beam, and means operative thereupon for passing a pulse to the anode of the discharge device to complete the connection of the calling line and a link finder with the selected link.

9. The system according to claim 7, and means controlled by the actuated selector for releasing the actuated link finder and associated register.

10. The system according to claim '7, and in which the link finder is a discharge device having which the selector comprises a normally blocked electric discharge device, having anode, cathode and grid electrodes, a grid circuit for said device controlled by the actuated line finder, an oscillator associated with the selector, means for synchronizing said oscillator with the sweep of the cathode ray tube, and means operative thereupon for passing a pulse to the anode of the device to complete the connection of the selected link over the selector to the called line.

12. The system according to claim '7, and in which the selector comprises a normally blocked electric discharge device, having anode, cathode and grid electrodes, a grid circuit for said device controlled by the actuated line finder, an oscillator associated with the selector, means for synchronizing said oscillator with the sweep of the cathode ray tube, and means operative thereupon for passing a pulse to the anode of the device to complete the connection of the selected link over the selector to the called line, and means operative thereupon for releasing the actuated dial link and associated register.

13. The system according to claim 7, and in which the link finder comprises a normally blocked electric discharge device having anode, cathode and grid electrodes, a grid circuit for said device controlled by the actuated line finder, an oscillator associated with the link finder, means for synchronizing said oscillator with the sweep of the cathode ray tube beam, and means operative thereupon for passing a pulse to the anode of the discharge device to complete the connection of the calling line and a link finder with the selected link, a normally inoperative pulse receiver in the register responsive to the operation of the calling device, and means actuated upon the synchronization of said oscillator for rendering said pulse receiver operative.

14. The system according to claim 7, and in which the selector comprises a normally blocked electric discharge device, having anode, cathode and grid electrodes, a grid circuit for said device controlled by the actuated line finder, an oscillator associated with the selector, means for synchronizing said oscillator with the sweep of the cathode ray tube, and means operative thereupon for passing a pulse to the anode of the device to complete the connection of the selected link over the selector to the called line, a normally inoperative switching means associated with the operated line finder for establishing a talking circuit to the called line, and means actuated upon' the synchronization of said oscillator for rendering said switching means operative.

15. In a telephone exchange system, a plurality of numerically designated lines, a calling device for each line operable in accordance with the number of the called line, a first cathode ray tube having electrodes in which said lines terminate, means for causing the beam of said tube to sweep over said electrodes, a plurality of normally inactive electronic line finders, a link associated with each line finder, means responsive to the initiation of a call for actuating a line finder to connect the calling line with the associated link whenever the beam of the tube engages the terminals of the line, a normally inactive electronic selector for each link, register means variably operated under the control of the calling device for controlling said selectors, a second cathode ray tube having an electrode for each link and means for causing its beam to sweep over the electrodes in a predetermined relationship to the sweep of the first tube, and means for actuating the selector of the link connected with the calling line whenever the beam of the first tube engages the terminals of the called line and the beam of the second tube sweeps over the electrode of the selected link.

16. The system according to claim 15, and in which the last-mentioned means for actuating the selector comprises means controlled by the first tube for producing signal pulses of a certain duration, and means controlled by the second tube for producing link identification pulses of longer duration.

17. The system according to claim 15, and in which the last-mentioned means comprises a multi-electrode discharge device having an output circuit controlling the actuating of the selector, an oscillator for applying potentials to one electrode of the device at a rate corresponding to the sweep of the first tube, a circuit for applying potentials to a second electrode of the device controlled by the register means, and a circuit for applying potentials to a third electrode of said device controlled by the second cathode ray tube.

18. In a telephone exchange system, a plurality of numerically designated lines, a calling device for each line operable in accordance with the number of the called line for controlling the setting up of a connection, a cathode ray tube having electrodes in which said lines terminate means for causing the beam of said tube to sweep over said electrodes, a plurality of normally inactive electronic lino finders. a link associated with each line finder, means responsive to the initiation of a call for actuating a line finder to connect the calling line with the associated link whenever the beam of the tube engages the terminals of the line, a normally inactive electronic selector for each line, normally inactive register means variably operated under the control of the calling device for controlling said selectors, means for seizing and connecting the register means with the selected link, means operative thereupon for preventing the seizure of the register means by another calling line, and means for actuating the selector of the selected link whenever the beam of the tube engages the terminals of the called line.

19. The system according to claim 18, and means operable upon the actuation of said selector for releasing the register means.

20. In a telephone exchange system, a plurality of numerically designated lines, a callin device for each line operable in accordance with the number of the called line, a cathode ray tube having electrodes in which said lines terminate, means including a master oscillator for causing the beam of said tube to sweep over said-electrodes, a plurality of normally inactive electronic.

line finders, a link associated with each line finder, 'a first oscillator associated with each line finder, means responsive to the initiation of a call for actuating a line finder, means operative thereupon for synchronizing the first oscillator of the actuated line finder to connect the calling line with the associated link whenever the beam of the tube engages the terminals of the line, a normally inactive electronic selector for each link, a plurality of registers variably operable under the control of the calling device and controlling said selectors, a link finder for each register, a second oscillator associated with each link finder, means operable upon the synchronization of the first oscillator for operating a link finder, means operative thereupon for synchronizin the second oscillator of the operated link finder with the master oscillator, a third oscillator for each selector, and means for synchronizing the third oscillator of the selector of the selected link with the master oscillator.

21. In a telecommunication system, a plurality of lines, an exchange at which said lines terminate and comprising links over which calling and called lines may communicate, means for establishing cyclically recurring time channels during which a calling line may utilize a link, a selector for each link, means at the exchange including a register common to said links for operating the selector 0! the link taken into use by the calling line to connect the called line therewith, means operable upon the completion of connection for releasing the register, and means operable upon the termination of the communication for releasing the line finder and selector employed therein.

22. The system according to claim 21, and in which each link has a line finder for connecting it with the calling line during a time channel.

23. The system according to claim 21, a line finder for each link, means operative upon the initiation of a call for connecting the line finder of a link to connect it with the calling line during a time channel reserved for the calling line, and means controlled by the register for operating the selector of the link taken into use to connect it with the called line during a time channel reserved for the latter.

24. The system according to claim 23, and means associated with the link for delaying communication signals from one of the interconnected lines until the occurrence of the time channel reserved for the other line.

DAVID HIRAM RANSOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,379,715 Hubbard July 3, 1945 2,387,018 Hartley Oct. 16, 1945 

